Flexible, armoured pipe and use of same

ABSTRACT

An armoured flexible pipe consists of an inner liner ( 3 ), on the inside of which a carcass ( 1 ) is provided, while the outer side of the inner liner is surrounded by a layer of pressure armour and a layer of tensile armour, which in turn are surrounded by one or more layers of thermally insulating bands which are shielded from the surroundings by an outer sheath. With the object of ensuring a sufficiently low transport of heat through the walls of the pipe, on the outside of the pressure and tensile armour layers ( 5, 6, 7, 8 ) thermally insulating bands are provided, which bands are made of a polymer or a polymeric composition, such as a polymer containing at least 50% polypropylene. The armoured flexible pipe according to the invention is especially advantageous for use in the extraction, transport or refining of mineral oil or related fluids.

The invention concerns an armoured flexible pipe comprising an innerliner which is provided on the inside with a carcass, while the outsideof the inner liner is surrounded by a pressure armour and a tensilearmour, which in turn is surrounded by one or more layers of thermallyinsulating bands which are shielded from the surroundings by an outersheath.

The invention also concerns a use of the pipe.

Pipes of the above-mentioned type normally comprise an inner liner,which forms a barrier against the outflow of the fluid, which isconveyed through the pipe. The inner liner is wound with one or morearmour layers which are not chemically bound to the inner liner butwhich can move in relation thereto, which ensures the flexibility of thepipe during laying out and operation.

Around the armour layers an outer sheath is provided with the object offorming a barrier against the ingress of fluids from the pipesurroundings to the armour layers. In order to prevent the collapse ofthe inner liner, this is often provided on the inner side with aflexible, wound pipe, a so-called carcass.

The above-mentioned type of flexible pipes is used, among other things,for the transport of fluids and gases in different depths of water. Theyare used especially in situations where very high or varying waterpressure exists along the longitudinal axis of the pipe. As examples canbe mentioned riser pipes which extend from the seabed up to aninstallation on or near the surface of the sea. Pipes of this type arealso used between installations, which are located at great depths onthe seabed, or between installations near the surface of the sea.

The armour layers, which are used as pressure armour, are most oftenconstructed in such a way that they comprise different metallicprofiles. When wound with a large angle in relation to the longitudinalaxis of the pipe, these profiles will be able to absorb radial forcesresulting from outer or inner pressure on the pipe. Among other thingsthe profiles thus prevent the pipe from collapsing or exploding as aresult of pressure, and are thus called pressure-resistant profiles.

Conversely, profiles, more specifically, tensile armour layers, whichare wound with a small angle in relation to the longitudinal axis of thepipe, will not be able to absorb radial forces to any significantdegree, but on the other hand are able to absorb forces exerted alongthe longitudinal axis of the pipe. Consequently, profiles of this typeare known as tension-resistant profiles.

Together, the tension-resistant profiles and the pressure-resistantprofiles form the armour for the pipe. In the armouring layer there alsoexists a free volume of such configuration that this can be ventilated,whereby a destructive build-up of pressure as a result of diffusion doesnot arise.

A problem in connection with the use of pipes of the type describedabove is that the transport of heat through the walls of the pipe can bequite considerable. With certain uses this is critical, since this typeof pipe is often used to transport fluids, which are desired to be heldat a temperature, which deviates from that of the surroundings. As anexample of such a use can be mentioned that of transporting crude oilbetween two installations. If the temperature of the crude oil fallsbelow a certain critical limit, mineral wax or solid hybrids can beformed in the pipe, which results in stoppages in the pipe.

In order to hold the transport of heat through the walls of the pipe atan acceptable level, it is known to wind one or more layers of bandsmade of a so-called syntactic foam on the outside of the pipe'stension-resistant armour, but on the inside of the outer sheath. Thisfoam contains a great amount of filling material in the form of hollowglass balls, which have very great resistance against crushing, and apolymeric matrix material. Syntactic foam possesses a low heatconductivity coefficient, whereby the application of this materialreduces the transport of heat through the walls of the pipe to anacceptable level.

However, the use of syntactic foam involves a number of limitations, themost important of which is that the mechanical strength of the foamoften becomes that factor which limits the areas of application of thepipe. The syntactic foam thus possesses very great resistance againsthydrostatic crushing, but only limited resistance against deformationand damage by local mechanical influences. A second problem connectedwith the use of syntactic foam is that the long-term characteristics ofthis material can be problematic to predict.

It is the object of the present invention to provide an armouredflexible pipe whereby a sufficiently low transport of heat through thewalls of the pipe is ensured, and where there is no substantial additionof inorganic filling materials.

The object of the invention is achieved in that the thermally insulatingbands are provided between the outer sheath and the tensile armour, andare made of a polymer or a polymeric mixture. It must further be notedthat the use of polymers or polymeric mixtures for the bands involves amuch cheaper and far easier processing of the bands than is the casewith the use of e.g. syntactic foam.

Suitable compositions and dimensions of the thermally insulating bandsare disclosed in the claims 2-4.

As mentioned, the invention also concerns a use of the pipe. This use isdisclosed in more detail in claim 5.

The invention will now be described in more detail with reference to thedrawing which comprises only one FIGURE, and which shows theconstruction of an armoured flexible pipe according to the inventionwith its various layers.

The FIGURE thus shows a pipe, which comprises an inner liner 3, whichsurrounds a carcass 1 consisting of a helically wound metal strip. Thiscarcass forms an inner, permeable pipe of great mechanical strength.During manufacture, the metal strip 2 is formed with flaps, which engagewith each other so that they hereby lock the individual windings of themetal strip 2 together in such a manner that the carcass 1 can be bentin its longitudinal direction.

Since the inner carcass 1 in itself is not impermeable, the purpose ofthe surrounding inner liner 3 is to prevent fluids from flowing into orout of the inside of the pipe. On the outside of the inner liner 3, oneor several layers of profiles 5,6 are wound in a helical manner, saidprofiles forming windings with a large angle in relation to thelongitudinal direction of the pipe. As a consequence of the large angle,the profiles are primarily able to absorb radial forces, which arise asa result of inner or outer pressure. The inner pressure arises duringoperation of the pipe. The outer pressure arises partly as a result ofthe hydrostatic pressure of the surroundings, and partly as a result ofmechanical influences during the laying of the pipe. The windings thusform a pressure armour which prevents the inner liner 3 and thethermally insulating layers from exploding as a result of high pressureon the inside of the pipe, or from collapsing as a result of highpressure on the outside of the pipe.

From the FIGURE it will also be seen that a tensile armour consisting ofone or several layers 7,8 being wound in a helical manner is provided onthe outside of the pressure armour 5,6.

Between the pressure armour and the tensile armour an intermediatesheath (not shown in the FIGURE) can be provided, the function of whichis to prevent fluids from migrating between the tensile armour and thepressure armour.

In order to increase the resistance against thermal transporttransversely through the walls of the pipe, according to the inventionon the outside of the armour layers a layer 10 can now be applied, saidlayer consisting of bands which are made of a homogenous material withlow thermal transmission coefficient, such as a polymer or a polymericcomposition. These layers are finally surrounded by an outer sheath 9.

Moreover, it should be noted that in addition to its thermallyinsulating characteristic, the thermally insulating layer must fulfil anumber of other requirements, cf. below.

As a result of the outer pressure on the pipe, the outer sheath and thelayer of thermally insulating band will be able to be pressed into thearmour layer. If the thermally insulating layer is pressed out betweenthe armouring strips, this will reduce the flexibility of the pipe to aconsiderable degree, with a possible destruction of the pipe as aconsequence. Therefore, it is important that the thermally insulatinglayer possesses the necessary mechanical strength, so that it is notcrushed or critically deformed during manufacture, laying-out andoperation of the pipe.

In accordance with a particularly preferred embodiment, the thermallyinsulating bands disclosed here are made of a homogenous plasticmaterial containing a minimum of 50-wt % polyolefin (PP).

In accordance with a second particularly preferred embodiment, thethermally insulating bands disclosed here are made of a homogenousplastic material containing a minimum of 50-wt % polyketones, such ase.g. Carilon produced by Shell.

What is claimed is:
 1. Armoured flexible pipe comprising an inner liner(3), on the inside of which a carcass (1) is provided, while the outerside of the inner liner is surrounded by one or more layers of pressure(5,6) and tensile (7,8) armour, which in turn is surrounded by one ormore layers of thermally insulating bands (10), which are shielded fromthe surroundings by an outer sheath (9), characterized in that thethermally insulating bands (10) are provided between the outer sheath(9) and the tensile armour (7,8), and are made of a polymer or apolymeric mixture.
 2. Armoured flexible pipe comprising an inner liner(3), on the inside of which a carcass (1) is provided, while the outerside of the inner liner is surrounded by one or more layers of pressure(5,6) and tensile (7,8) armour, which in turn is surrounded by one ormore layers of thermally insulating bands (10), which are shielded fromthe surroundings by an outer sheath (9), characterized in that thethermally insulating bands (10) are provided between the outer sheath,and in that the thermally insulating bands (10) are made of a polymerwith a polyolefin content of at least 50%.
 3. Armoured flexible pipecomprising an inner liner (3), on the inside of which a carcass (1) isprovided, while the outer side of the inner liner is surrounded by oneor more layers of pressure (5,6) and tensile (7,8) armour, which in turnis surrounded by one or more layers of thermally insulating bands (10),which are shielded from the surroundings by an outer sheath (9),characterized in that the thermally insulating bands (10) are providedbetween the outer sheath, and in that the thermally insulating bands(10) are made of a polymer with a polyketon content of at least 50%. 4.Armoured flexible pipe according to claim 1, characterized in that thebreadth of the insulating bands lies in the interval 10-100 mm.
 5. Useof an armoured pipe according to claim 1 for the extraction, transportor refining of mineral oil, gas or related fluids.
 6. In an armouredflexible pipe of the type comprising an outer sheath forming a barrieragainst ingress of fluid from the pipe surroundings, and an inner linerforming a barrier against the outflow of fluid conveyed through thepipe, the inner liner being surrounded by one or more armour layers ofmetallic profiles which are not chemically bound to the inner liner butwhich can move in relation thereto, the improvement comprising thermallyinsulating bands of a polymer or a polymeric mixture provided betweenthe armour layer or layers and the outer sheath, and in direct contactwith at least one layer of the armour layer or layers.